Method VALDATION

Method validation is the process used to confirm that the analytical procedure employed for a specific test is suitable for its intended use. Results from method validation can be used to judge the quality, reliability and consistency of analytical results; it is an integral part of any good analytical practice.
Analytical methods need to be validated or revalidated

before their introduction into routine use;

whenever the conditions change for which the method has been validated (e.g., an instrument with different characteristics or samples with a different matrix); and

whenever the method is changed and the change is outside the original scope of the method.

The validity of a specific method should be demonstrated in laboratory experiments using samples or standards that are similar to unknown samples analyzed routinely. The preparation and execution should follow a validation protocol, preferably written in a step-by-step instruction format. Possible steps for a complete method validation are listed in Table 1. This proposed procedure assumes that the instrument has been selected and the method has been developed. It meets criteria such as ease of use; ability to be automated and to be controlled by computer systems; costs per analysis; sample throughput; turnaround time; and environmental, health and safety requirements.

What is validation?

ISO/IEC 17025 definition: ‘The confirmationby examination and the provision of objective evidencethat the particular requirements for a specific intended use are fulfilled’

What is validation?

Specific intended use
– analytical requirement
– what will test method be used for? why are measurements required?

Without validation there can be no assurance that results will be fit for purpose

When do you validate a method?

During method development
– is the proposed method likely to be fit for purpose?Before using any method for analysis of test samples
– including standard/published methods which have been validated by others
– verify suitability for analytical requirement
– verify own ability to match published dataChange of application/working environment/analystFollowing period of non-use

ISO/IEC 17025 Selection of methods and method validation

§5.4.1 General
– laboratory shall use appropriate methods and procedures for all tests within its scope

§5.4.2 Selection of methods
– methods must meet customer requirements
– preference for standard methods (international/national standards)
– ‘laboratory shall confirm that it can properly operate standard methods before introducing the tests’
– laboratory-developed methods may be used if they are validated

Extent of validation

As extensive as necessary for applicationMust record validation data and document procedures usedInclude statement of ‘fitness for purpose’Method performance must be relevant to customer needs and assessed against intended use of the method
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measurement uncertainty, detection limit, selectivity, linearity, repeatability/reproducibility, robustness

Method performance parameters

Selectivity/specificity
– am I measuring what I think I’m measuring? are there any interferences?Precision (repeatability, reproducibility)
– how close are the results of replicate measurements made on the same sample?Bias, recovery
– how close are the results to the ‘right’answerWorking range
– range of analyte concentrations that can be measured reliably
– limit of detection, limit of quantitationRuggedness/robustness
– control necessary for each stage of the procedure

Depends on the criticality of the measurement, scope of the method, level of information and experience already available

Fitness for purpose

Analyse data from method performance parametersAre target values achieved?
– YES - method is fit for purpose
– NO - more development requiredMethod is validated by the declaration of fitness for purpose

Summary

Method validation is required to produce meaningful data

Both in-house and standard methods require validation/verification

Key requirement of ISO/IEC 17025

Validation should be a planned activity
– parameters required will vary with application